Motor control device and electric power steering device

Abstract

The motor control device includes: a d-axis current command value calculation unit configured to set a first d-axis current command value for field-weakening; a first current limiting unit configured to calculate a first q-axis current command value by limiting a base q-axis current command value as to satisfy a condition of motor rated current; a second current limiting unit configured to calculate a second d-axis current command value and a second q-axis current command value by limiting the first d-axis current command value and the first q-axis current command value, respectively to satisfy and not exceed an allowable upper limit battery current; voltage command value calculation units configured to calculate voltage command values, based on the second d-axis current command value and the second q-axis current command value; and a voltage limiting unit configured to prevent saturation of a duty ratio by limiting the voltage command values.

The invention claimed is: 
     
       1. A motor control device comprising:
 a torque control unit configured to set a base q-axis current command value to control torque generated by a motor; 
 a d-axis current command value calculation unit configured to set a first d-axis current command value for field-weakening, based on the base q-axis current command value and rotational velocity of the motor; 
 a first current limiting unit disposed in a succeeding stage of the d-axis current command value calculation unit and configured to calculate a first q-axis current command value by limiting the base q-axis current command value according to the first d-axis current command value in such a way that driving current of the motor does not exceed a rated current of the motor; 
 a second current limiting unit disposed in a succeeding stage of the first current limiting unit and configured to calculate a second d-axis current command value and a second q-axis current command value by limiting the first d-axis current command value and the first q-axis current command value, respectively in such a way that output current from a battery does not exceed a predetermined allowable upper limit; 
 a voltage command value calculation unit configured to calculate a first d-axis voltage command value and a first q-axis voltage command value, based on the second d-axis current command value and the second q-axis current command value; 
 a voltage limiting unit configured to calculate a second d-axis voltage command value and a second q-axis voltage command value by limiting the first d-axis voltage command value and the first q-axis voltage command value, respectively in such a way as to prevent saturation of a duty ratio in PWM control based on the first d-axis voltage command value and the first q-axis voltage command value; and 
 a drive circuit configured to drive the motor, based on the second d-axis voltage command value and the second q-axis voltage command value. 
 
     
     
       2. The motor control device according to  claim 1 , wherein the d-axis current command value calculation unit calculates the first d-axis current command value according to a q-axis current command value obtained by limiting the base q-axis current command value in such a way that driving current of the motor does not exceed a rated current of the motor, based on a past value of the second d-axis current command value. 
     
     
       3. The motor control device according to  claim 1 , wherein the d-axis current command value calculation unit calculates the first d-axis current command value according to a q-axis current command value obtained by limiting the base q-axis current command value in such a way that output current from the battery does not exceed the allowable upper limit, based on a past value of the second d-axis current command value. 
     
     
       4. The motor control device according to  claim 1 , wherein the d-axis current command value calculation unit limits an upper limit of the first d-axis current command value, based on rotational velocity of the motor. 
     
     
       5. The motor control device according to  claim 1 , wherein
 the voltage limiting unit includes: 
 a voltage upper limit setting unit configured to set a voltage upper limit, the voltage upper limit being an upper limit of applied voltage to the motor; and 
 a voltage limiting gain setting unit configured to set a voltage limiting gain according to the voltage upper limit, and 
 calculates a second d-axis voltage command value and a second q-axis voltage command value by limiting the first d-axis voltage command value and the first q-axis voltage command value, respectively according to the voltage limiting gain. 
 
     
     
       6. The motor control device according to  claim 5 , wherein the voltage upper limit setting unit sets a voltage upper limit, based on at least one of a voltage equivalent to use efficiency improvement achieved by superimposing a third-order harmonic on polyphase voltage command values of the motor, the motor being a polyphase motor, a voltage drop due to dead time, and a reduction in a ratio of motor terminal voltage to a duty ratio due to dead time compensation. 
     
     
       7. The motor control device according to  claim 5 , wherein
 the voltage limiting unit: 
 includes a disturbance voltage suppression unit configured to output a first multiplication result obtained by multiplying a sum of the first d-axis voltage command value and output from a first delay element by the voltage limiting gain and a second multiplication result obtained by multiplying a sum of the first q-axis voltage command value and output from a second delay element by the voltage limiting gain and also input the first multiplication result and the second multiplication result to the first delay element and the second delay element, respectively; and 
 outputs the second d-axis voltage command value including the first multiplication result and the second q-axis voltage command value including the second multiplication result. 
 
     
     
       8. The motor control device according to  claim 7 , wherein the voltage limiting gain setting unit sets the voltage limiting gain, based on the voltage upper limit, the sum of the first d-axis voltage command value and output from the first delay element and the sum of the first q-axis voltage command value and output from the second delay element. 
     
     
       9. The motor control device according to  claim 7 , wherein the voltage command value calculation unit outputs the first d-axis voltage command value and the first q-axis voltage command value including a d-axis integral component, the d-axis integral component being an integral component of deviation of a detected value of d-axis current in driving current of the motor from the second d-axis current command value, and a q-axis integral component, the q-axis integral component being an integral component of deviation of a detected value of q-axis current in driving current of the motor from the second q-axis current command value, respectively and suppresses the d-axis integral component and the q-axis integral component, based on the voltage limiting gain. 
     
     
       10. The motor control device according to  claim 7 , wherein
 the first d-axis voltage command value includes a feedforward d-axis voltage command value calculated by feedforward control based on the second d-axis current command value and a feedback d-axis voltage command value calculated by feedback control based on deviation of a detected value of d-axis current in driving current of the motor from the second d-axis current command value, 
 the first q-axis voltage command value includes a feedforward q-axis voltage command value calculated by feedforward control based on the second q-axis current command value and a feedback q-axis voltage command value calculated by feedback control based on deviation of a detected value of q-axis current in driving current of the motor from the second q-axis current command value, 
 the disturbance voltage suppression unit: 
 outputs the first multiplication result obtained by multiplying a sum of the feedback d-axis voltage command value and output from the first delay element by the voltage limiting gain and the second multiplication result obtained by multiplying a sum of the feedback q-axis voltage command value and output from the second delay element by the voltage limiting gain; and 
 inputs the first multiplication result and the second multiplication result to the first delay element and the second delay element, respectively, 
 the voltage limiting gain setting unit sets the voltage limiting gain, based on the voltage upper limit, a sum of the feedback d-axis voltage command value, output from the first delay element, and the feedforward d-axis voltage command value, and a sum of the feedback q-axis voltage command value, output from the second delay element, and the feedforward q-axis voltage command value, and 
 the voltage limiting unit outputs the second d-axis voltage command value including a third multiplication result obtained by multiplying the feedforward d-axis voltage command value by the voltage limiting gain and the first multiplication result and also outputs the second q-axis voltage command value including a fourth multiplication result obtained by multiplying the feedforward q-axis voltage command value by the voltage limiting gain and the second multiplication result. 
 
     
     
       11. An electric power steering device comprising:
 the motor control device according to  claim 1 ; and 
 wherein the electric power steering device provides a steering system of a vehicle with a steering assist force, using the motor.